The invention relates to an improved method and apparatus or device for execution of a piecing process on an open end spinning assembly, in which, controlled by a program control, a yarn end is taken from the spinning assembly and prepared, like the spinning assembly, for the piecing process, and in which there are operations engaging in the spinning assembly for execution of the piecing process, whereafter the pieced yarn is transferred to the spinning assembly.
In a known piecing device (German OS No. 2,360,296; corresponding U.S. Pat. No. 3,987,610), it is provided that the piecing device will first execute preparatory operations in which the broken yarn end is taken from a winding device and brought inside the piecing device in a prepared condition and then brought into the zone of a yarn draw-off passage of a spinning assembly, in which passage the prepared yarn end is held ready for the actual piecing process. Preparatory operations on the spinning assembly, such as cleaning or the like, may also belong to the preparatory operations. For the subsequent execution of the actual piecing process, the piecing device provides that sliver feed will occur in a suitable way, and that the prepared yarn end will be led back into the spinning rotor and then drawn off again. This entails engagement or control of the sliver feed device. Moreover, there is intervention in the rotor drive, to make use of the circumstance that the spinning rotor, in running up to its operational rotational speed (rpm--revolutions per minute), passes through a range that is particularly favorable for piecing. The pieced yarn is subsequently transferred by a transfer device to the spinning assembly. The switching in points and the period of switching in of the individual elements of the piecing device are controlled by a program control. This piecing device has results that in themselves are satisfactory, i.e. piecings are obtained whose tear strength and appearance are such that they can be accepted in the produced yarn without need to clear these pieced places from the yarn.
However, in practice it has been determined that despite acceptable functioning of the piecing device, pieced places with different appearance and different quality occur on the individual spinning assemblies, where in extreme cases it even goes so far that the piecing process fails, so that no yarn can be pieced. This is essentially apparently caused by the fact that the mechanical devices of the spinning assembly that are controlled by the piecing device in the course of the piecing process have to be switched or utilized in other ways, to be distinguished as to functioning with respect to the other individual spinning assemblies. For example, it is to be observed that because of manufacturing tolerances there are slight deviations in the working of the feed devices and also in the running up behavior of the spinning rotors at the respective spinning assemblies of a given spinning machine. These unavoidable differences that are caused by manufacturing tolerances must be taken into account in design of the piecing device in such a way that, in spite of these deviations, there will be an adequate reliability in piecing. This means that in many cases, with previously contemplated piecing apparatus, thicker pieced places will be produced than would actually be necessary or desirable.
The invention deals with the problem of creating a process of the type in question whereby the percentage of successful piecing operations will be improved, and also the quality of the pieced places will be improved so far as possible. The invention contemplates providing that the pieced yarn is checked for the presence and/or the quality of the pieced place, and that depending upon the test results or detected parameters, transfer to the spinning assembly will occur or the piecing process will be interrupted with subsequent repetition of the piecing operation, whereby there will be a changed program control in the repeated piecing process, at least for the operations that engage in the spinning assembly.
By the process according to the invention, at least the reliability of the piecing operation will be substantially increased, if, for example, the piecing process has failed and there is no pieced place, the program control will automatically be so changed that a socalled "safety piecing" will be obtained, so that continued operation is possible. This feature of the invention is here based on the determination by the inventors that it is not very worthwhile to repeat a piecing operation with the same program if this piecing operation has once failed. It is basically not to be expected then that a substantially better result would come from the second attempt.
With use of the different programs, tolerance-caused deviations between the individual spinning assemblies can be balanced out in such a way that essentially there will be the production of uniform piecings at all assemblies. It is a question of optimization of the design of the control element here, whether only the reliability of the piecing device will be increased, or whether there will also be improvement in the quality of the piecing. If only reliability is to be increased according to certain preferred embodiments of the present invention, it suffices in most instances to make relatively simple changes in the program control. If, however, the quality of the yarn piecing is to be taken as the decisive criterion according to certain other preferred embodiments of the present invention, then in some situations a number of piecing tests will have to be effected with various changes in the program control.
If, for example, the piecing process has failed, it may be because not enough sliver was fed into the spinning rotor to make a sufficiently thick sliver ring. This could be taken into account according to the present invention by a change in the program control that advances the time for start of sliver delivery. If, with this program change, the repeated piecing process were to fail again, its cause could be a poor quality of the yarn end supplied to the spinning rotor. It could be that, shortly before the yarn break which is supposed to now be corrected by the piecing operation, there was already a poor yarn being produced. In this case, for the third piecing attempt, another program change could be provided according to the present invention, so that the preparatory operation would involve a longer yarn length being wound off and only thereafter would there be preparation of the yarn end for the piecing process.
Embodiments of the invention are also contemplated where it is provided that the control element will automatically decide, in dependence of the result of testing of the piecing or determination of the absence of a piecing, in what way the program needs to be changed. If, for example, a greater or less quantity of sliver should be delivered and/or other work steps should occur earlier or later or be sustained for a longer period, the control element will react accordingly. However, it may also be provided according to other preferred embodiments of the invention, that the control element will always transmit the same signal, indpendently of the occurring defects, said signal triggering a specified series of experimental program changes with respective individual piecing attempts.
In an advantageous embodiment of the invention, a device for execution of the process is created in that a control element is provided for checking the pieced yarn and/or the pieced place in the yarn, which is connected via a pickup with the program control which is equipped with control elements controlled by the pickup, for interruption and repetition of the piecing process and also with switching elements controlled by the pickup which elements are connected to work programs in the program control which differ from one another, for devices for execution of the piecing process.
In order to avoid that a plurality of piecing trials will have to be undertaken in each piecing operation, in an advantageous embodiment of the inention, it is provided that the switching device is connected with the signal output of a storage in which there is stored a switching signal that is associated with the successful work program of the spinning assembly in question. This means then, that an attempt to effect a piecing after a yarn break on a spinning assembly will be made with the work program that is identical with the work program that was successful for eliminating the previous yarn break at this spinning assembly.
Advantageously, an optically, capacitively, or inductively operating yarn testing head acts as control element, being disposed in the yarn path for the pieced yarn and determining variations in cross-section of the yarn. Here it is advantageous if the said yarn test head is as close as possible to the spinning assembly because then when there is a defect not too much yarn will have run into the piecing device, or onto the spool of the spinning assembly. In order to provide a qualitative determination with respect to the piecing and thereafter to allow automatic decisions to be made near the program control, it is provided in certain preferred embodiments that a signal transmitter connected to the yarn testing head will convert the measurement of the yarn testing head into signals that are associated with the time of appearance of the pieced place in the testing head and/or the thickness of the pieced place and/or the length of the pieced place.
Because the difficulties to be avoided by the present invention essentially are caused by differences in the individual spinning assemblies, it is provided in an advantageous embodiment of the invention that the work programs will differ with reference to time of switch-in and/or duration of the switched-on period of a device for delivery of sliver and/or a device to start the run up of the spinning rotor and/or a device for carrying the yarn end back into the spinning rotor and for drawing off the pieced yarn again. Then only that part of the program control will be changed that concerns the operations which in any way are dependent upon the function of the individual spinning assembly.
These and further objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.